西加毒素在海洋食物链传递之关键因子研究

The benthic dinoflagellate, Gambierdiscus spp. produces polyether toxins that cause ciguatera fish poisoning (CFP) in humans. The toxins initially enter food webs when fish forage on macroalgae, or other substrates, hosting this epiphytic dinoflagellate. A frequently observed and well-documented pattern is the occurrence of outbreaks following reef disturbances by coral bleaching. Global warming, ocean acidification, eutrophication and overfishing are the major factors causing coral bleaching. It is hypothesized that disturbances that provide space on dead sections of coral suitable for colonization by filamentous algae, providing more habitat and enabling the proliferation of epiphytic dinoflagellates during the pattern of succession. Hence, there is significant concern that the incidence of CFP will increase as reefs continue to degrade due to coral bleaching events and other anthropogenic disturbances. In this context, we propose to study of the key factors that influence the flux of ciguatera toxins through marine food webs. The palatability of these macroalgal hosts to herbivorous fishes may also play a role in the propagation of ciguatera. Macroalgal species that are preferentially or rapidly consumed by herbivorous fish may increase their growth rates, and these species could be sources of high toxin levels even at low dinoflagellate densities. In contrast, widely occurring but unpalatable species with much higher Gambierdiscus spp. densities may contribute little to toxin flux. Quantification of the interaction mechanisms between the macroalga and dinoflagellate in order to describe their mutual relationship will also allow for the prediction of CTX fluxes. Furthermore, the toxicity of individual Gambierdiscus strains can vary dramatically, meaning that an area can have a high or low ciguatera risk depending on which genetic strains are dominant. Therefore, it is important to understand not only genetic diversity in the source organisms and food web transfer, but also the resistant mechnisms of these fishes. Understanding the flux of CTXs at different trophic levels will contribute to the characterization of the determinants of ciguatera toxicity that are relevant to the management of marine resources and mitigation of incidences of CFP throughout tropical and subtropical areas.

西加毒素是一类强毒性聚醚类毒素,源自纲比甲藻, 经食物链传递而蓄积于各种食用珊瑚鱼体内，进而危及消费者安全。由于缺乏简便、准确的监测手段，携毒珊瑚鱼误入市场，致使人体中毒事件时有发生。本项目拟从研究西加毒素在海洋食物链关键传递因子着手, 去剖析西加毒素的扩散在高发海区有着相对静态的空间分布，而西加毒素的组成及含量在不同高发地区鱼类的体内则有着明显的动态变化的現象。通过不同分析手段，对珊瑚礁生态系统中蓄含西加毒素的草食性鱼类进行摄食藻类的多样性分析，筛选出其所嗜食的藻类，进而对其所粘附底栖微藻进行鉴定与分析，通过研究毒素合成与环境介质的关系，确定鱼体内毒素来源及组成。从而在不同食性层次(Trophic level)确立简易、可信及准确的「西加毒素标示性生物」,建立从个体外推到群落乃至生态系统的风险评价体系，在西加鱼毒素的监测、控制、预警方面，树立新观念及新理论。

西加毒素是一种高度氧化的大分子聚醚类毒素，最初由海洋底栖甲藻纲比甲藻合成弱极性前体化合物冈比亚毒素，并通过食物链传递并生物积累，接着在各种珊瑚鱼体内合成高毒性的西加毒素（Ciguatoxins, CTX），进而会引发西加鱼毒中毒事件（Ciguatera seafood poisoning），从而危害消费者安全，每年有50000人左右因食用含有西加毒素的海产品而中毒。由于缺乏简便、准确的检测手段，携毒珊瑚鱼误入市场，致使人体中毒事件时有发生。由于西加毒素的特殊地位，引起了学者们较多的关注。.本项目主要包括四部分内容。第一部分研究了珊瑚礁鱼类肌肉以及血液中的西加毒素。具体来说，建立了一种定量分析鱼类血液中这三种西加毒素方法。还开发了一种平行震荡方法萃取海鳗鱼肉中的西加毒素，同时采用高效液相色谱-电喷雾串联质谱法同时测定三种西加毒素包括P-CTX-1、P-CTX-2和P-CTX-3的残留量。第二部分主要从研究西加毒素在海洋食物链关键传递因子着手，检测了西加毒素在珊瑚礁食物网中的分布，证实了蓄含西加毒素鱼类主要分布于马拉基岛的西边海域。通过分析食物网中不同鱼类肌肉组织的西加毒素组成，揭示了食性层次与P-CTX-1之间存在微弱但显著的正相关关系。此外，还通过SIAR法检测了珊瑚鱼类的摄食多样性。第三部分主要对纲比甲藻基里巴斯株系进行了分类鉴定以及毒素鉴定，并研究了纲比甲藻在马拉基岛的分布及丰度，同时掌握了不同pH值和波长对纲比甲藻生长及产毒的影响。第四部分通过研究太平洋型西加毒素对海洋鳉鱼类生理以及行为的影响，发现随着西加毒素剂量的增大，鳉鱼开始会出现异常运动和生理变化。.研究结果将为更加全面地了解西加毒素在食物链的传递过程提供了依据，为我国底栖甲藻的进一步研究提供参考，同时也为有害藻华的减灾防灾提供科学依据，在保护海洋科学环境和人类健康方面也具有积极意义。